Tower Design and Manufacture - Small Wind Turbines: Analysis, Design, and Application - page 224

1 = 2

1
2ph 3 = 2

3EI
m t þ m tt

n 1 ¼

16. The tower being raised in Fig. 10.10 has a diameter of 30 cm and a wall
thickness of 4 mm. It is 13 m high. With the turbine and tower material data
as in Table 10.2 , calculate the maximum wind speed it could withstand as a
monopole.
17. Why is a gin pole (Figs. 10.2 and 10.10 ) necessary for raising and lowering by
cable?
18. Explain why the tower in Fig. 10.10 would exert no overturning moment on
its foundations while it is being raised or lowered?
19. Notice that the tail fin on the turbine in Fig. 10.10 is hinged. The hinge has
high damping. How might this effect the natural frequency and damping ratio
of the turbine yaw response?
20. Towers with a nearly circular cross-section can be subject to peridoic vortex
shedding when the wind blows. Tall chimneys, for example, often have spiral
additions to break up this shedding which causes a side force that is small but
nearly periodic at a frequency f in Hz given by St = fd/U & 0.2. St is called
the Strouhal number. What is the relationship between k, R, and d if f coin-
cides with 1P? For the two-bladed Aerogenesis 5 kW turbine with a design
k = 9, and the tower dimensions given in Table 10.2 is f likely to coincide
with 1P? What might be the consequences of any coincidence?
21 It is usually argued that interference effects between turbines in close prox-
imity are due to the loss of kinetic energy in the wind received by the
downwind turbine(s) after passing through the upwind one(s). How would you
estimate the contribution of tower drag to this interference?

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